The subject matter disclosed herein relates to a combustor for a gas turbine, and more specifically to a combustor where oxidizer and fuel are injected by a fuel nozzle that creates a recirculation zone for anchoring a burning zone.
Gas turbines generally include a compressor, a combustor, one or more fuel nozzles, and a turbine. Working fluid enters the gas turbine through an intake and is pressurized by the compressor. The working fluid may be pure air or low-oxygen or oxygen-deficient content working fluid. Some examples of a low-oxygen content working fluid include, for example, a carbon dioxide and steam based mixture and a carbon-dioxide and nitrogen based mixture. The compressed working fluid is then mixed with fuel supplied by the fuel nozzles. The working fluid-fuel oxidizer mixture is supplied to the combustors at a specified ratio for combustion. The oxidizer may be air, pure oxygen, or an oxygen enriched fluid. The combustion generates pressurized exhaust gases, which drive the blades of the turbine.
The combustor includes a burning zone, a recirculation zone or bubble, and a dilution zone. An end cover of the combustor typically includes one or more fuel nozzles. In an effort to provide stable and efficient combustion, sometimes a pilot burner or nozzle can be provided in the end cover as well. The pilot nozzle is used to initiate a flame in the burning zone. Fuel is evaporated and partially burned the in the recirculation bubble, and the remaining fuel is burned in the burning zone. Removing or reducing the recirculation bubble results in the working fluid-flow mixture expanding within the combustor, which decreases residence time of the working fluid-fuel mixture.
The presence of a strong recirculation bubble can be especially important in stoichiometric diffusion combustion applications where a low-oxygen or oxygen-deficient content working fluid is employed such as, for example, during oxy-fuel combustion. When combusting in low-oxygen working fluid applications, it is important that combustion is complete before a significant amount of fuel and oxidizer escape the flame zone. A strong recirculation bubble with a secondary small recirculation will ensure that increasing residence time in the flame zone will achieve high combustion efficiency. Therefore, it would be desirable to provide a fuel nozzle that promotes stable and efficient combustion, especially in applications where a low-oxygen content working fluid is employed.